In a closed type aluminum electrolytic condenser or an electric double layer type condenser or the like, an opening portion of a pressure container receiving an element main body thereof is closed by a sealing plate sealed via a gasket. In the case of the complete sealing structure as mentioned above, there is a risk that internal pressure of the container is increased on the basis of a Joule heat generation in the case that a sudden load is applied, whereby reduction in function and reduction in service life are caused. Accordingly, there has been conventionally developed a structure which can release a gas generated in the container, by forming a notch in a bottom portion of the pressure container so as to provide a rupture plate, or mounting a rubber cap to a cover so as to provide a safety valve, thereby preventing the pressure container from being ruptured, or by mounting a breather having the function of transmitting the gas and not transmitting the liquid to a sealing plate by the way of applying a water repelling treatment to a porous membrane made of, for example, PTFE or the like so as to release the internal pressure of the container.
In accordance with the prior art, in the case that the sealing plate has the rupture plate or the safety valve, once the container is ruptured, the sealing plate can not be used thereafter, whereby it is impossible to use the sealing plate repeatedly.
Further, the breather provided in the sealing plate has a function of keeping the internal pressure of the pressure container constant, and preventing an internally sealed liquid such as an electrolytic solution or the like from leaking, however, since the gas within the container is discharged slightly from the breather even by heat and internal pressure generated in a normal use state, the electrolytic solution tends to be reduced due to evaporation, and water vapor tends to make an intrusion from the external. Further, under a bad environment, there is a case that the porous membrane of the breather generates clogging, and it is hard to expect a stable performance. Further, since the breather can not respond to a sudden internal pressure increase, it is necessary to provide additionally with an explosion proofing valve for releasing the internal pressure in a moment of time in the case that the internal pressure becomes a predetermined value or more and preventing the container from being exploded.
The present invention is made by taking the points mentioned above into consideration, and a technical object of the present invention is to provide a pressure release valve which can securely achieve a pressure release function repeatedly because the pressure release valve is not broken due to a pressure release at a time when an internal pressure is increased, in addition to a breather function of preventing a sealed liquid from being evaporated and preventing foreign matter from making an intrusion from the external.